Numbness of the left arm may be related to physiological factors, or may be caused by cervical spondylosis, cerebrovascular disease and other reasons. 1. Physiological factors: such as long time engaged in lifting heavy physical labor, or sleeping on the left side of the arm for a long time under pressure, may affect the blood circulation of the left side of the arm, which in turn causes numbness in the left arm. 2. Cervical spondylosis: Commonly found in patients with cervical osteophytes and cervical disc herniation. Because of the neck for a long time to maintain an incorrect posture, easily lead to hyperplasia of the bone or herniated cervical intervertebral disc compression of the local nerve root, may cause numbness in the left arm, may also be accompanied by hand pain, weakness and other symptoms. 3. Cerebrovascular disease: commonly seen in mild cerebral hemorrhage, or due to local cerebrovascular hemorrhage or ischemia, resulting in lesions in the area of cerebral nerve damage, causing cerebral dysfunction, which may cause numbness in the left arm, may also be accompanied by numbness of the left side of the lower limbs, weakness and other symptoms. Left arm numbness, may also be caused by other reasons, if the symptoms persist, should be taken seriously, as soon as possible to seek medical treatment, diagnose the cause of the disease, give targeted treatment.